Effect of surface roughness and complex indices of refraction on polarized thermal emission

Abstract

We present a series of measurements characterizing the dependence of polarized thermal emission on surface roughness. In particular, we measure the spectrally resolved degree of linear polarization (DOLP) for a series of roughened borosilicate (Pyrex) glass substrates as a function of the roughness parameter Ra, the root-mean-square slope distribution, and observation angle theta. Also measured are a series of smooth glass substrates coated with two particular polymers of interest, i.e., a common commercially available Krylon paint and a chemical-agent-resistant coating paint. The DOLP is measured over a 4-13 microm wave band by using a modified Fourier transform IR spectrometer in which a wire-grid polarizer and a quarter-wave Fresnel rhomb are used in conjunction to measure all four Stokes parameters. In addition, we show an enhanced DOLP due to anomalous dispersion exhibited by the surface material.

Enhanced material identification using polarimetric hyperspectral imaging

“…The shaded region represents plus/minus one standard deviation across the 48 retrieved index of refraction values at each wavelength. The green line denotes the true index of refraction taken from [21]. Note that while the retrieved values differ from the true values, they are very consistent, even with changing surface temperature.…”

“…The downwelling radiance is expected to be blackbody-like at the ambient temperature of the room. The fits were performed twice, holding both surface temperature and downwelling temperature fixed, and another allowing them to vary ±50 K. The results of these two fits, along with the true index of refraction value, taken from [21], are shown in Figure 2.…”

LWIR polarimetry for enhanced facial recognition in thermal imagery

“…There has been growing interest among researchers investigating polarization-based thermal imaging techniques in which information inherent in the image forming radiance is retained and displayed as a 2D image, i.e., thermal polarimetric imaging [1][2][3][4][5]. It is known that both manmade and naturally occurring materials/objects emit radiation in the thermal IR that exhibits a preferential linear polarization state that is orthogonal to reflection-induced polarization [6].…”

Enhanced facial recognition for thermal imagery using polarimetric imaging

“…There has been growing interest among researchers investigating polarization-based thermal imaging techniques in which information inherent in the imageforming radiance is retained and displayed as a 2D image, i.e., thermal polarimetric imaging [1][2][3][4][5]. It is known that both man-made and naturally occurring materials/objects emit radiation in the thermal IR that exhibits a preferential linear polarization state that is orthogonal to reflectioninduced polarization [6].…”

“…where I0, I90, I45, and I−45 represent the measured radiant intensity of the linear states (measured relative to the vertical), at angles 0°, 90°, 45°, and −45°, respectively, and IR and IL represent the right-and left-handed circularly polarized radiant states. For radiance that is total or partially polarized, we define a degree-of-total-polarization (DoP) image as DoP S1 2 S2 2 S3 2 p S0 ; (5) where 0 ≤ DoP ≤ 1.…”